bash

dpkg-query -Wf '${Installed-Size}\t${Package}\n' | sort -n | tail -n 10 

lists 10 largest packages on a system

dpkg --list |grep "^rc" | cut -d " " -f 3 | xargs sudo dpkg --purge

purges leftover configuration files from already uninstalled programs

echo "scale=10000;4*a(1)" | bc -l

computes pi to 10000th decimal place using bc commandline calculator

(free -m | grep Mem | awk '{print "RAM Used: "$3" | Total: "$2}';free -m | grep Swap | awk '{print "SWAP Used: "$3" | Total: "$2}') |tr '\n' ' | '

free memory monitor

echo $RANDOM

od -A n -t d -N 2 /dev/urandom | tr -d ' '

openssl rand 16 | od -DAn

various commands to get a random integer number

save below as temps.sh and give it executable rights (chmod +x ./temps.sh):

1. #!/bin/bash

2. show_temp1(){(echo "ACPI:";sensors | grep -A 0 "temp1:" | cut -c16-19)}

3. show_cpu_temp(){(echo "CPU";sensors | grep -A 0 "Core" | cut -c16-19)}

4. show_thermal_zone0(){

5. x=$(</sys/class/thermal/thermal_zone0/temp)

6. temp=$((x / 1000))

7. echo "thermal_zone0 "$temp

8. }

9. (show_temp1;echo "C |";show_cpu_temp;echo "C |";show_thermal_zone0;echo "C") |tr '\n' ' | '

simple script for monitoring system temperatures

vnstati --vsummary --hsummary -i eno1 -o ./summary.png;firefox ./summary.png

generates .png image with various network adapter statistics using firefox and vnstati

How to compile stuff from source (in general,  basic flow):

1) unpack a tarball: tar zxvf prog.tar.gz or tar jxvf prog.tar.bz2

2) ./configure && make && sudo make install

or ./autogen.sh && make && sudo make install

dpkg architecture commands:

dpkg --print-architecture - current architecture, main architecture

dpkg --print-foreign-architectures - other architectures installed on a system

dpkg --remove-architecture

note before removing architecture with dpkg you have to remove all of that

architecture's packages.

sudo apt-get purge ".*:i386" for example for i386

then

dpkg --remove-architecture i386

listing i386 packages

dpkg -l | grep i386

this works similar for other architectures installed on the system, just replace i386 with different architecture's name

system install date:

usually you would want to install package like tuptime right after having installed your fresh OS. But if you could not or are working on a system where you can not install such package, see below commands how to deduce when the system was installed:

first run ls -lact --full-time /etc | tail

then compare the oldest file with ls -lact --full-time / | tail

and finally ls -lact --full-time /var | tail

then if the oldest file is a file you can further check it with

stat FILE | grep Change

on a system that lack GNU Coreutils don't use --full-time.

disk erase (double-check if the drive you are erasing is the right one or you risk of loss of your valuable data!):

fdisk -l # check for disk name

hdparm -I /dev/sdb # disk info

if the drive is not frozen:

hdparm --user-master u --security-set-pass p /dev/sdb # set temporary password

if the drive is frozen:

put the computer to sleep and wake it up

echo -n mem > /sys/power/state

if the disk supports the secure erase enhanced:

hdparm --user-master u --security-erase-enhanced p /dev/sdb

if not

hdparm --user-master u --security-erase p /dev/sdb

after waiting for the process to finish check again with

hdparm -I /dev/sdb if the password is reset and drive state back to normal

to zero-fill a drive

sudo dd if=/dev/zero of=/dev/sdb bs=1M status=progress

to random fill a drive

sudo dd if=/dev/urandom of=/dev/sdb bs=1M status=progress

then verify with

dd if=/dev/sdb bs=1M count=128 for nothing or random output

sudo shred -v -n1 /dev/sdb # overwrite with random data using shred

watch -n1 "df -BM && sensors" 

simple monitoring of free disk space and system temperatures